Questions tagged [coins]

Puzzles involving the manipulation of coins as physical objects inside a set of rules.

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12
votes
12answers
5k views

Coin Game with infinite paradox

Here’s the puzzle/problem: Let’s presume we are best friends. I own the house next to you. I make a gaming proposition along the following lines: You throw a coin over and over again. So long as it ...
6
votes
3answers
231 views

Finding both fake coins in a set of $5$

There are $5$ rupees on Arnav's table. He knows that exactly $2$ of the rupees are counterfeit. One of these $2$ coins is lighter than a normal (non-counterfeit) rupee, and one of these $2$ coins is ...
5
votes
4answers
228 views

Coin Removal Variation

A variation on this problem, where coins can become neighbors. There is a line of $n$ coins on the table, all showing either heads or tails. The object of the puzzle is to remove all the coins by a ...
12
votes
3answers
2k views

Coin removal problem

I have a slight variation of the coin flipping problem. There is a line of $n$ coins on the table; some of them are heads up and the rest are tails up, in no particular order. The object of the ...
4
votes
3answers
198 views

Riffing off of Dudeney

Attributed to H.E. Dudeney, the following puzzle is possibly the world's most recognized coin rearrangement puzzle. So it is a mystery to me why the two related puzzles that follow can't be found ...
2
votes
1answer
104 views

Bet with coin, empty glass bottle and cork

You have a coin, an empty glass bottle and a cork. If you throw the coin into the bottle and close up the bottle with the cork, how can you pull out the coin, without pulling out the cork or smashing ...
9
votes
3answers
466 views

The Dollar Bill

Bill was asked to form as many triangles on top of a flat table using his 5 pennies (3 coins on the table where centers are connected by imaginary lines to make a triangle). His teacher told him that ...
3
votes
1answer
114 views

Shiny Smooth Coins [duplicate]

You are blindfolded, and there are a number of shiny, smooth coins in front of you. One side is purple and the other side is green. Your friend tells you, once, the number of purple coins there are. ...
16
votes
7answers
4k views

Five Men and Four Coins Puzzle

This is a puzzle of five men guessing how many stars will appear from tossing four coins. There are five men: Mr. Zero, Mr. One, Mr. Two, Mr. Three, and Mr. Four; playing with four coins. For each ...
4
votes
1answer
332 views

Fake and genuine coins

There are 14 coins, numerated from 1 to 14, and presented as an evidence at the court. The first 7 are fake coins, and others are genuine coins. Fake coins have all the same weight and they are ...
8
votes
2answers
396 views

Counterfeit Detector

You have a machine that lights up if counterfeit coin is placed in it. Any number of coins can be placed in the machine. It only lights up and does not indicate how many counterfeit coins are present (...
1
vote
2answers
266 views

The Monster and the Chessboard [duplicate]

You have a standard checkerboard with 64 squares and a coin in each square, randomly facing heads or tails up. There is an evil monster in the room with you and he arbitrarily selects some square and ...
6
votes
2answers
663 views

Bag of gold coins weighing with a digital scale

We are given 100 bags, each with 200 coins. All but one of the bags are filled with identical gold coins, but the other bag contains fake coins. The fakes all weigh the same as each other, but weigh ...
1
vote
1answer
196 views

Logic Coin Question [duplicate]

Please view comments to see how it is not a duplicate.... I am looking at it from a CPU perspective. If there are 23 coins that are on a screen, and there are two players and you get to pick if you ...
13
votes
3answers
3k views

68 coins with 100 weighings

You have 68 coins of different weights. Using only a balance scale and the coins themselves, find the heaviest and lightest of the coins with only 100 comparisons. This puzzle is adapted from The ...
1
vote
1answer
758 views

The swap puzzle

The swap puzzle Place small coins heads up on the squares marked H and tails up on the squares marked T. Swap the positions of the Heads for the Tails in as few moves as possible. There are two ways ...
7
votes
6answers
2k views

How will Y lose the game?

X and Y are playing a game. There are eleven coins on the table and each player must pick up at least one coin but not more than five in a turn. The person picking up the last coin loses. X starts. ...
1
vote
1answer
464 views

Interactive Coin Puzzle

We see the standard version of the puzzle in: The Puzzle That's HARDER After Seeing the Solution! Which corresponds to the case $n=2$ in my follow up problem. 5 coin puzzle In short, you ...